Elevator load bearing member

ABSTRACT

A load bearing member ( 34 ) for supporting an elevator car ( 10 ) has a plurality of tension members ( 38 ) that bear the weight and counterweight of the elevator car ( 10 ). The plurality of tension members extends along a length. An outer cover ( 42 ) envelopes the plurality of tension members and has a first surface and a second surface. The plurality of tension members are sandwiched between the first surface ( 46 ) and the second surf ace ( 48 ). The first surface is for traction on a sheave ( 22 ). The first surface and the second surface define a cross-section ( 52 ) transverse to the length of the load bearing member. The cross-section has a first end portion ( 56 ), a middle portion ( 60 ) and a second end portion ( 64 ). The middle portion has a first width (w 1 ) between the first surface and the second surface which is smaller than a second width (w 2 ) between the first surface and the second surface of one of the first end portion and the second end portion.

BACKGROUND OF THE INVENTION

This invention generally relates to a belt for supporting an elevatorcar.

An elevator has a car that is raised and lowered by a motor. Typically,a counterweight is used to offset the weight of the car so that the loadon the motor is reduced. A belt connects the car to the counterweightand rests on a sheave. The belt obtains traction on the sheave, which isturned by the motor. Typically, the belt for the elevator car iscomposed of belt cords that support the weight of the elevator. Thesebelt cords are very stiff along their length and are surrounded by abelt jacket that obtains traction on the sheave.

It has long been known in the industry that using a crown on a sheavewill help the belt track toward the center of the sheave, even when thebelt is slightly misaligned. While the crown may help the belt trackbetter, the crown can degrade its performance. Specifically, due to theshape of the crown, pressure at the interface between the sheave and thebelt is non-uniform. A high peak pressure will exist at the top of thecrown, resulting in reduced life of the belt jacket and the belt cords.

In addition, because of the stiffness of the belt cords, these cordstend to move at the same speed. The speed of the sheave surface isdirectly proportional to the distance between a centerline of the sheaveand its surface. Consequently, the peak of the crown travels at a highercircumferential speed than the remainder of the sheave surface. Becausethe belt cords all move at the same speed, and the speed of the sheavesurface varies due to the crown, there are locations where the beltsurface and the corresponding sheave surface will have different speeds.As a consequence, there is localized slipping between the belt surfaceand the sheave surface, resulting in belt wear.

A need therefore exists for a belt having a profile that accommodatesthe shape of the crown of the sheave.

SUMMARY

A belt for supporting an elevator car has tension members that bear theweight and counterweight of the car. The tension members extend along alength. An outer cover envelopes the plurality of tension members. Theouter cover has a first surface and a second surface. The first surfaceprovides traction for a sheave. The second surface may contact idlersheaves associated with reverse bending. The tension members aresandwiched between the first surface and the second surface. The firstsurface and the second surface define a cross-section transverse to thelength of the tension members. The cross-section has a first endportion, a middle portion and a second end portion. The middle portionhas a first width between the first surface and the second surface thatis smaller than a width between the first surface and the second surfaceof either the first end portion or the second end portion.

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic view of an elevator, showing elevatorcar, counterweight, sheaves and load bearing member.

FIG. 2 illustrates a front view of a sheave of FIG. 1.

FIG. 3 illustrates a cross-sectional view of the load bearing member ofFIG. 1.

FIG. 4 illustrates a cross-sectional view of the load bearing member ofFIG. 3 atop the sheave of FIG. 2.

FIG. 5 illustrates a graph of an increase of slip rate relative to beltposition for a prior art flat belt.

FIG. 6 illustrates contact pressure across the belt width of a prior artflat belt.

FIG. 7 illustrates contact pressure across the belt width of a flat beltcompared to the inventive belt.

FIG. 8 is a cross-section of a prior art belt design.

FIG. 9 is a view of the prior art belt design of FIG. 8 atop a crown ofa sheave.

FIG. 10 is a front view of another sheave of FIG. 1.

FIG. 11 is a view of an alternatively shaped crown.

FIG. 12 is a view of another crown.

FIG. 13 is a view of another inventive belt design.

DETAILED DESCRIPTION

Illustrated in FIG. 1 is a schematic view of a traction elevator 8. Theelevator 8 includes an elevator car 10 having weight 14, a counterweight18, a motor 30 and first sheave 22, a traction sheave. The elevator car10 is suspended by load bearing member 34. Tension members 38 extendalong length L of load bearing member 34, a belt for example. Loadbearing member 34 is driven by first sheave 22 and motor 30 and islooped across second sheaves 26 as known. Further, load bearing member34 couples the weight of counterweight 18 to elevator car 10 havingweight 14 so as to at least offset the weight 14 of elevator car 10.

FIG. 2 illustrates a front view of first sheave 22, a traction sheave,which is rotatable by motor 30 about axis A. In this particular sheave,first sheave 22 has multiple contact surfaces 23, 24 and 25, which areconvex and adapted to engage through friction three separate loadbearing members 34. As shown, each contact surface 23, 24, 25 has acrown C₁, C₂ and C₃, respectively. Each crown C₁, C₂ and C₃ has a radiusR₂.

In the past, a load bearing member was typically flat as shown incross-section by FIG. 8. This figure shows flat belt 84 in cross-sectionacross its length. Flat belt 84 has first end portion 70, middle portion78 and second end portion 74 across cross-section 68. Across the lengthof flat belt 84 are a plurality of tension members 38, such as steelcords, sandwiched between first surface 72 and second surface 76 ofouter cover 80. The width W_(uniform) between first surface 72 andsecond surface 76 is uniform.

First surface 72 obtains traction on first sheave 22. Due to the curvedshape of a crown, Poisson's ratio effects and loading, the geometry offlat belt 84 changes when disposed on first sheave 22, as shown in FIG.9. There, flat belt 84 is shown disposed on first sheave 22, havingcrown C₁. As shown, flat belt 84 has changed from a flat shape to acurved shape.

With reference to FIG. 9, because of the stiffness of tension members38, tension members 38 will move at about the same speed, V_(belt), whenfirst sheave 22 rotates in use. For example, first sheave 22 rotatesabout axis A, at say angular speed ⊖. At point T, crown surface 73 isdistance N from axis A while at point Q, crown surface 73 is distance Mfrom axis A, which is a distance greater than distance N. Therefore, thevelocity of crown surface 73 at point T is Vt=N×⊖ while the velocity ofcrown surface 73 at point Q is Vq=M×⊖. Because M is greater than N, thevelocity of crown surface 73 at point Q, V_(q), is greater than thevelocity of crown surface 73 at point T, Vt. Flat belt 84 will tend tomove with first sheave 22 at point Q because the pressure is greaterthere. However, with reference to FIG. 5, flat belt 84 will then slip atthe edges because V_(belt)=V_(q), which is greater than V_(t). The sliprate at point T is approximately V_(belt)−V_(t).

Wear rate is a function of pressure multiplied by slip rate and ishighest near the outer edges where there is high slip and moderatepressure. Consequently, non-uniform wear results leading to greater wearat the edges than at the middle of flat belt 84. These differences alsoresult in tension members 38 changing length due to strain at differentlevels, again causing non-uniform wear on flat belt 84. In addition, asshown in FIG. 6, for any given load on the belt, the load on flat belt84 tends to be greater at the middle of the belt than compared to theend of the cross-section of the belt. As a consequence, flat belt 84will wear unevenly.

FIG. 3 illustrates an example of the inventive load bearing member. Loadbearing member 34 is shown in cross-section 52 transverse to length L ofload bearing member 34 as shown in FIG. 1. Load bearing member 34 hasouter cover 42 having first surface 46 and second surface 48, whichenvelops or at least partially covers tension members 38, heresandwiched between first surface 46 and second surface 48. Tensionmembers 38 may be, for example, steel cords. Each of the tension members38 extends for the length L of load bearing member 34 and is shown alsoin cross-section by FIG. 3. Load bearing member 34 has cross-section 52defined by first surface 46 and second surface 48. Cross-section 52 hasfirst end portion 56, middle portion 60 and second end portion 64.

Generally, the shape of load bearing member 34 is matched to crown C₁and tension members 38 are disposed between first surface 46 and secondsurface 48 so as to ensure that they extend along a line parallel toaxis A when placed and loaded on first sheave 22. Accordingly, in FIG.3, first surface 46 forms first curve 47 while second surface 48 formssecond curve 49. Both curves are concave. First surface 46 is fortraction on first sheave 22 and generally matches the curved shape of acrown, such as crown C₁, of first sheave 22.

With reference to FIG. 4, load bearing member 34 has first curve 47having first radius R₁. First sheave 22, the traction sheave, has acrown with second radius R₂. First radius R₁ is at least equal to R₂although R₁ may be greater than R₂. Middle portion 60 has first width W₁while first end portion 56 and second end portion 64 have second widthW₂. First width W₁ is smaller than second width W₂.

As a consequence of this design, when load bearing member 34 is placedatop first sheave 22, the plurality of tension members 38 tend to extendacross cross-section 52 in a linear fashion along axis A of first sheave22. Tension members 38 are all about distance X from axis A, includingat points T and Q. Then, when first sheave 22 rotates load bearingmember 34, the plurality of tension members 38 will rotate about thesame distance X from axis A so that tension members 38 will all have thesame velocity, resulting in reduced slippage of load bearing member 34across cross-section 52. In addition, tension members 38 will maintainthe same length. By keeping the same length, the strain andcorresponding stress on tension members 38 are equal. Slippage is alsoreduced and a more uniform pressure across load bearing member 34results, reducing wear. Accordingly, outer cover 42 is shaped to fillthe space between tension members 38 and first sheave 22 so that theyrotate at the same distance X from axis A when load bearing member 34 isdisposed on first sheave 22 and supporting weight 14 and counterweight18.

In addition, as shown in FIG. 7, contact pressure is distributed moreuniformally across load bearing member 34. For example, when firstradius R₁ is equal to second radius R₂, that is, the radius of the firstsurface 46 is equal to the radius R₂ of first sheave 22, a relativelyflat distribution of pressure is achieved across the crown of firstsheave 22, such as crown C₁. In addition, when first radius R₁ isgreater than R₂, the distribution of pressure is also relatively flatcompared to the distribution of force across a flat belt.

FIG. 10 illustrates a front view of second sheave 26. Like first sheave22, second sheave 26 has contact surfaces 23, 24 and 25. One surface,such as contact surface 23, contacts load bearing member 34 along secondsurface 48. Each contact surface 23, 24 and 25 has crowns surfaces C₁,C₂ and C₃. Crown C₁ has radius R₄, for example, relative to axis A.

With reference to FIG. 3, second surface 48 is for contact with secondsheave 26 for reverse bending of load bearing member 34 and generallymatches the curved shape of a crown, such as crown C₁, of second sheave26. Second surface 48 forms a concave curve, second curve 49, having athird radius R₃, which is at least equal to, if not greater than, radiusR₄ of crown C₁ of sheave 26. In this way, wear from contact with secondsheave 26 can be also reduced like the wear from contact with firstsheave 22.

In addition, although crowns C₁, C₂ and C₃ of second sheave 26 are shownas identical to crowns of first sheave 22, they may differ. For example,second sheave 26 could have crown C₄, a parabolic shaped curve, as shownin FIG. 12 or crown C₅, having straight ramps 107 with curved peak 109,as shown in FIG. 11, while first sheave 22 could have crowns C₁, C₂ orC₃. Alternatively, first sheave 22 could have the crowns C₄ and C₅ whilesecond sheave 26 could have crown C₁, C₂ or C₃.

Then, for example, with reference to FIG. 13, load bearing member 100has first surface 46 having shape 104 to match crown C₁ of first sheave22 and has second surface 48 having shape 105 to match crown C₄, aparabolic curve. Each shape 104 and 105 thereby ensures tension members38 will rotate at the same distance from axis of rotation H of eachrespective sheave. Shape 104 ensures this equidistant rotation oftension members 38 with respect to first sheave 22 while shape 105ensures equidistant rotation of tension members 38 with respect tosecond sheave 26.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this invention. The scope of legal protection given tothis invention can only be determined by studying the following claims.

1-20. (canceled)
 21. A load bearing member for supporting an elevatorcar, comprising: a plurality of tension members for bearing the weightand counterweight of an elevator car, said plurality of tension membersextending along a length; an outer cover at least partially coveringsaid plurality of tension members; said outer cover having a firstsurface and a second surface, said plurality of tension memberssandwiched between said first surface and said second surface, saidfirst surface for traction on a sheave; wherein said first surface andsaid second surface define a cross-section transverse to said length,said cross-section having a first end portion, a middle portion, and asecond end portion; wherein said middle portion has a first widthbetween said first surface and said second surface smaller than a secondwidth between said first surface and said second surface of one of saidfirst end portion and said second end portion; and wherein one of saidplurality of tension members in said middle portion is spaced closer tosaid first surface than another of said plurality of tension members inone of said first end portion and said second end portion.
 22. The loadbearing member of claim 21 wherein said first width is smaller than saidsecond width of both said first end portion and said second end portion.23. The load bearing member of claim 21 wherein said first surfacedefines at least a first curve.
 24. The load bearing member of claim 23wherein said first curve has a first radius at least equal to a secondradius of a crown of the sheave prior to loading said outer cover on thesheave.
 25. The load bearing member of claim 24 wherein said firstradius is greater than said second radius.
 26. The load bearing memberof claim 21 wherein said first surface defines a first shape matching asecond shape of a crown of the sheave prior to loading of said outercover on the sheave.
 27. The load bearing member of claim 26 whereinsaid first shape locates said plurality of tension members across awidth of the sheave to be about equally distant from an axis of rotationof the sheave when said outer cover is disposed on a crown of thesheave.
 28. The loading bearing member of claim 23 wherein said secondsurface defines at least a second curve.
 29. The loading bearing memberof claim 28 wherein said first curve is shaped differently than saidsecond curve.
 30. A load bearing member for supporting an elevator car,comprising: a plurality of tension members for bearing the weight andcounterweight of an elevator car, said plurality of tension membersextending along a length; an outer cover at least partially coveringsaid plurality of tension members; said outer cover having a firstsurface and a second surface, said plurality of tension memberssandwiched between said first surface and said second surface, saidfirst surface for traction on a sheave, said first surface and saidsecond surface defining a cross-section transverse to said length;wherein said outer cover has a cross-sectional shape such that saidplurality of tension members are spaced across said cross-sectionalshape about equally from an axis of rotation of the sheave when disposedon a crown of the sheave; and wherein said first surface defines atleast a first curve and said second surface defines at least a secondcurve, and wherein said first curve and said second curve are concave,at least one of said plurality of tension members entirely sandwichedbetween said first curve and said second curve.
 31. The load bearingmember of claim 30 wherein said first curve has a first radius at leastequal to a second radius of the crown of the sheave.
 32. The loadbearing member of claim 31 wherein said first radius is greater thansaid second radius.
 33. The load bearing member of claim 30 wherein saidsecond curve has a third radius at least equal to a fourth radius of acrown of another sheave.
 34. An elevator, comprising: an elevator carhaving a weight; a counterweight for at least partially offsetting saidweight; at least one sheave for moving said elevator car, said at leastone sheave having a crown; a plurality of tension members for bearingsaid weight and said counterweight of said elevator car, said pluralityof tension members extending along a length and arc of said plurality oftension disposed entirely above said crown; an outer cover envelopingsaid plurality of tension members; said outer cover having a firstsurface and a second surface, said plurality of tension memberssandwiched between said first surface and said second surface, saidfirst surface for traction on a sheave; wherein said first surface andsaid second surface define a cross-section transverse to said length,said cross-section having a first end portion, a middle portion, and asecond end portion; and wherein said middle portion has a first widthbetween said first surface and said second surface smaller than a secondwidth between said first surface and said second surface of one of saidfirst end portion and said second end portion.
 35. The elevator of claim34 wherein said first surface defines at least a first curve.
 36. Theelevator of claim 35 wherein said first curve has a first radius atleast equal to a second radius of a crown of the sheave.
 37. The loadbearing member of claim 35 wherein said first curve is concave.
 38. Theloading bearing member of claim 35 wherein said second surface definesat least a second curve for contacting another sheave.
 39. The loadingbearing member of claim 38 wherein both said first curve and said secondcurve are concave.